Theoretical Bicycle question
Discussion
I am aware this may seem a little far-fetched but I was thinking about this the other day. Hopefully this is the correct place for this.
Here is the scenario: You have a flat runway, it is totally smooth and there are no imperfections or gradients in it. To make things a bit more simple as I would not want distance to be the limitation the length of it is infinite.
There is a bicycle and with every crank of the pedals you begin to accelerate. With every push of the pedals you gain speed and once your legs are moving too fast you can change up a gear and begin the process again. This bicycle is equipped with many gears, I wouldn't want a finite number of gears to be the issue limiting top speed - so again it has infinite gears.
Is there a theoretical top speed you can hit on this bike? Would it be possible to hit 200 mph for example?
I am aware there will be things to work against; notably drag, the human effort to gain speed with a massive gear, the tyres. So what will stop the cyclist from hitting such high speeds?
Here is the scenario: You have a flat runway, it is totally smooth and there are no imperfections or gradients in it. To make things a bit more simple as I would not want distance to be the limitation the length of it is infinite.
There is a bicycle and with every crank of the pedals you begin to accelerate. With every push of the pedals you gain speed and once your legs are moving too fast you can change up a gear and begin the process again. This bicycle is equipped with many gears, I wouldn't want a finite number of gears to be the issue limiting top speed - so again it has infinite gears.
Is there a theoretical top speed you can hit on this bike? Would it be possible to hit 200 mph for example?
I am aware there will be things to work against; notably drag, the human effort to gain speed with a massive gear, the tyres. So what will stop the cyclist from hitting such high speeds?
Well there's more to it than that and looking at the rules I read this:
"3.2.2.1 200 Meter Speed Trial: The winner of this event shall be the vehicle achieving the highest average speed over a 200 meter interval. A flying start from any distance is permitted, within practical limits as established by the event organizer."
So who knows what practical limits are set at. He had a 5 mile run up, but if he had 10 he may have been able to go faster - that isn't the maximum theoretical speed of a bike. Obviously finding an arrow straight surface to ride down for 100 miles isn't realistic but i'd like to put that aside for the time being.
"3.2.2.1 200 Meter Speed Trial: The winner of this event shall be the vehicle achieving the highest average speed over a 200 meter interval. A flying start from any distance is permitted, within practical limits as established by the event organizer."
So who knows what practical limits are set at. He had a 5 mile run up, but if he had 10 he may have been able to go faster - that isn't the maximum theoretical speed of a bike. Obviously finding an arrow straight surface to ride down for 100 miles isn't realistic but i'd like to put that aside for the time being.
g4ry13 said:
I am aware there will be things to work against; notably drag, the human effort to gain speed with a massive gear, the tyres. So what will stop the cyclist from hitting such high speeds?
Drag! - and friction. As the gear ratio gets higher the torque gets lower.However if you elimate drag by conducting the experiment in a vacuum, the cyclist will fall off dead so you're no further forward (literally!)
no, there is a new record holder on the top speed on a push bike.
Guy Martin - 112.somethingorother MPH.
done on a beach.
watch Speed with Guy Martin. he did it as part of a tv show
http://www.channel4.com/programmes/speed-with-guy-...
watch that video on there
Guy Martin - 112.somethingorother MPH.
done on a beach.
watch Speed with Guy Martin. he did it as part of a tv show
http://www.channel4.com/programmes/speed-with-guy-...
watch that video on there
Edited by 4G63T on Monday 19th May 00:32
no, there is a new record holder on the top speed on a push bike.
Guy Martin - 112.somethingorother MPH.
done on a beach.
watch Speed with Guy Martin. he did it as part of a tv show
http://www.channel4.com/programmes/speed-with-guy-...
watch that video on there
Guy Martin - 112.somethingorother MPH.
done on a beach.
watch Speed with Guy Martin. he did it as part of a tv show
http://www.channel4.com/programmes/speed-with-guy-...
watch that video on there
Edited by 4G63T on Monday 19th May 00:32
Simpo Two said:
g4ry13 said:
I am aware there will be things to work against; notably drag, the human effort to gain speed with a massive gear, the tyres. So what will stop the cyclist from hitting such high speeds?
Drag! - and friction. As the gear ratio gets higher the torque gets lower.However if you elimate drag by conducting the experiment in a vacuum, the cyclist will fall off dead so you're no further forward (literally!)
It's simple.
The POWER generated by the rider is availiable to push with a forwards force.
The DRAG created by rolling friction (tyres, cogs chains, bearings rolling etc) and the aerodynamic drag (pushing air out of the way of the bike+rider) pushes backwards.
When those two forces are balanced, there is no remaining force to accelerate the bike any more, so the speed is constant.
For a bike, the aerodynamic forces are the important ones, which increase with the SQUARE of speed. This means doubling your speed takes 4 times as much power to do so.
Unfortunately, us humans are relatively puny! Most people would struggle to put out more than a couple of hundred watts for more than a few minutes!
With training top athletes can push peak power output up towards 1000W (for very short periods of time) and average power outputs around 400W for longer periods.
This practically limits the top speed of an "unassisted" bicycle somewhat (around 80mph currently)
Other records include "assistance" and that is what Guy Martin did. using a big truck with a large "shield" on it to try to remove the air resistance meanng that he only had to overcome the rolling friction drag. Even then, he only got to around 110mph iirc?
The POWER generated by the rider is availiable to push with a forwards force.
The DRAG created by rolling friction (tyres, cogs chains, bearings rolling etc) and the aerodynamic drag (pushing air out of the way of the bike+rider) pushes backwards.
When those two forces are balanced, there is no remaining force to accelerate the bike any more, so the speed is constant.
For a bike, the aerodynamic forces are the important ones, which increase with the SQUARE of speed. This means doubling your speed takes 4 times as much power to do so.
Unfortunately, us humans are relatively puny! Most people would struggle to put out more than a couple of hundred watts for more than a few minutes!
With training top athletes can push peak power output up towards 1000W (for very short periods of time) and average power outputs around 400W for longer periods.
This practically limits the top speed of an "unassisted" bicycle somewhat (around 80mph currently)
Other records include "assistance" and that is what Guy Martin did. using a big truck with a large "shield" on it to try to remove the air resistance meanng that he only had to overcome the rolling friction drag. Even then, he only got to around 110mph iirc?
g4ry13 said:
Here is the scenario: You have a flat runway, it is totally smooth and there are no imperfections or gradients in it. To make things a bit more simple as I would not want distance to be the limitation the length of it is infinite.
There is a bicycle...
Is there a conveyor belt involved, and at what speed, if ever, would the bicycle take off?There is a bicycle...
Max_Torque said:
It's simple...
For a bike, the aerodynamic forces are the important ones, which increase with the SQUARE of speed. This means doubling your speed takes 4 times as much power to do so.
Tut tut! You're playing fast and loose with your terminology here Max. The force increases with the square of the speed, but the POWER increases with the cube of the speed. A doubling of speed takes eight times as much power! By human standards, a mathematical brick wall.For a bike, the aerodynamic forces are the important ones, which increase with the SQUARE of speed. This means doubling your speed takes 4 times as much power to do so.
4G63T said:
no, there is a new record holder on the top speed on a push bike.
Guy Martin - 112.somethingorother MPH.
done on a beach.
watch Speed with Guy Martin. he did it as part of a tv show
http://www.channel4.com/programmes/speed-with-guy-...
watch that video on there
Different records with different rules. Guy did it behind a vehicle on a relatively conventional bike. Sebastian did it with nothing breaking the wind in front of him on a totally unconventional "bike"Guy Martin - 112.somethingorother MPH.
done on a beach.
watch Speed with Guy Martin. he did it as part of a tv show
http://www.channel4.com/programmes/speed-with-guy-...
watch that video on there
Edited by 4G63T on Monday 19th May 00:32
If we're including drag, the average person on an average bike will struggle to top 30. As others have mentioned, with various tricks you can get significantly higher.
An interesting (if you're a physics teacher) point to make here is the relation between torque and power. You can calculate it fairly easily, but here is an example of how much torque a cyclist can put out. It's about what a small car engine might (and, you will notice, most cyclists don't have quite as much mass to push around!).
So why aren't we tearing up drag strips on bikes and laughing at the puny slow cars? Well, partly because we can't sustain high outputs for very long, unlike an engine.
But another problem is how fast we can spin our legs - not very. Few people can get much above 150 RPM - bear in mind a motorbike engine might idle at ten times that.
So, to go faster, we change the gear ratio so the wheel spins more than once for every time we spin our legs (or we just use a really big wheel - same effect). The catch is, as you've noted, you have to press on the pedals harder (aka produce more torque) to maintain even the same speed in a higher gear.
This is where power comes in: we define power here as the product of torque (how hard you're pressing on the pedals, sort of) and angular velocity (how fast you spin your legs). The reason that's neat is that something like a gearbox, or differential, or wheel, does not change that number*: if you need 1000 watts (a little over 1 hp) to sustain 40mph, and you can't produce 1000 watts, you're not going to do 40mph today. If you have 1000 watts, then with the right gearbox, you can. For a cyclist, the right gearbox "gears up", with the wheel spinning (at best) over four times as fast as the crank (a typical "top speed" ratio is 53/11), but as a result the torque at the wheel is less than a quarter of what the cyclist produced. For a car or motorbike, the right gearbox "gears down", with the wheel spinning slower than the crank, but with more torque.
And that's where arguments about Audi diesels come from
An interesting (if you're a physics teacher) point to make here is the relation between torque and power. You can calculate it fairly easily, but here is an example of how much torque a cyclist can put out. It's about what a small car engine might (and, you will notice, most cyclists don't have quite as much mass to push around!).
So why aren't we tearing up drag strips on bikes and laughing at the puny slow cars? Well, partly because we can't sustain high outputs for very long, unlike an engine.
But another problem is how fast we can spin our legs - not very. Few people can get much above 150 RPM - bear in mind a motorbike engine might idle at ten times that.
So, to go faster, we change the gear ratio so the wheel spins more than once for every time we spin our legs (or we just use a really big wheel - same effect). The catch is, as you've noted, you have to press on the pedals harder (aka produce more torque) to maintain even the same speed in a higher gear.
This is where power comes in: we define power here as the product of torque (how hard you're pressing on the pedals, sort of) and angular velocity (how fast you spin your legs). The reason that's neat is that something like a gearbox, or differential, or wheel, does not change that number*: if you need 1000 watts (a little over 1 hp) to sustain 40mph, and you can't produce 1000 watts, you're not going to do 40mph today. If you have 1000 watts, then with the right gearbox, you can. For a cyclist, the right gearbox "gears up", with the wheel spinning (at best) over four times as fast as the crank (a typical "top speed" ratio is 53/11), but as a result the torque at the wheel is less than a quarter of what the cyclist produced. For a car or motorbike, the right gearbox "gears down", with the wheel spinning slower than the crank, but with more torque.
And that's where arguments about Audi diesels come from
4G63T said:
no, there is a new record holder on the top speed on a push bike.
Guy Martin - 112.somethingorother MPH.
done on a beach.
As much as a respect Guy for the balls needed to ride 112mph behind a truck it is neither the fastest slipstreaming cyclist ever nor IMO is it "proper" cycling.Guy Martin - 112.somethingorother MPH.
done on a beach.
The top slipstream record is- 166.944 mph by Fred Rompelberg, Bonneville Salt Flats, Utah, USA on 3 October 1995.
The record for the fastest bike is certainly Sebastiaan Bowier in his recumbent at Battle Mountain (83.13mph)
FWIW there is much debate about the 100mph barrier in recumbent/HPV circles, the problem is the available power (from a human) and the minimum size (and therefore drag) said human can squeeze into while still able to pedal and steer. Obviously no World class cyclist has ever made an attempt (although Sebastiaan Bowier and previous holder Sam Whittingham are no slouches) but I doubt a TdF level Tim Trialest would make much difference.
Given that I imagine if you combined the perfect weather and road with the perfect athlete and todays technology you might crack 90mph.
paranoid airbag said:
If we're including drag, the average person on an average bike will struggle to top 30. As others have mentioned, with various tricks you can get significantly higher.
An interesting (if you're a physics teacher) point to make here is the relation between torque and power. You can calculate it fairly easily, but here is an example of how much torque a cyclist can put out. It's about what a small car engine might (and, you will notice, most cyclists don't have quite as much mass to push around!).
So why aren't we tearing up drag strips on bikes and laughing at the puny slow cars? Well, partly because we can't sustain high outputs for very long, unlike an engine.
But another problem is how fast we can spin our legs - not very. Few people can get much above 150 RPM - bear in mind a motorbike engine might idle at ten times that.
So, to go faster, we change the gear ratio so the wheel spins more than once for every time we spin our legs (or we just use a really big wheel - same effect). The catch is, as you've noted, you have to press on the pedals harder (aka produce more torque) to maintain even the same speed in a higher gear.
This is where power comes in: we define power here as the product of torque (how hard you're pressing on the pedals, sort of) and angular velocity (how fast you spin your legs). The reason that's neat is that something like a gearbox, or differential, or wheel, does not change that number*: if you need 1000 watts (a little over 1 hp) to sustain 40mph, and you can't produce 1000 watts, you're not going to do 40mph today. If you have 1000 watts, then with the right gearbox, you can. For a cyclist, the right gearbox "gears up", with the wheel spinning (at best) over four times as fast as the crank (a typical "top speed" ratio is 53/11), but as a result the torque at the wheel is less than a quarter of what the cyclist produced. For a car or motorbike, the right gearbox "gears down", with the wheel spinning slower than the crank, but with more torque.
And that's where arguments about Audi diesels come from
An interesting (if you're a physics teacher) point to make here is the relation between torque and power. You can calculate it fairly easily, but here is an example of how much torque a cyclist can put out. It's about what a small car engine might (and, you will notice, most cyclists don't have quite as much mass to push around!).
So why aren't we tearing up drag strips on bikes and laughing at the puny slow cars? Well, partly because we can't sustain high outputs for very long, unlike an engine.
But another problem is how fast we can spin our legs - not very. Few people can get much above 150 RPM - bear in mind a motorbike engine might idle at ten times that.
So, to go faster, we change the gear ratio so the wheel spins more than once for every time we spin our legs (or we just use a really big wheel - same effect). The catch is, as you've noted, you have to press on the pedals harder (aka produce more torque) to maintain even the same speed in a higher gear.
This is where power comes in: we define power here as the product of torque (how hard you're pressing on the pedals, sort of) and angular velocity (how fast you spin your legs). The reason that's neat is that something like a gearbox, or differential, or wheel, does not change that number*: if you need 1000 watts (a little over 1 hp) to sustain 40mph, and you can't produce 1000 watts, you're not going to do 40mph today. If you have 1000 watts, then with the right gearbox, you can. For a cyclist, the right gearbox "gears up", with the wheel spinning (at best) over four times as fast as the crank (a typical "top speed" ratio is 53/11), but as a result the torque at the wheel is less than a quarter of what the cyclist produced. For a car or motorbike, the right gearbox "gears down", with the wheel spinning slower than the crank, but with more torque.
And that's where arguments about Audi diesels come from
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